PositioNZ Activity Round-up

30 September 2009

PositioNZ is LINZ's Global Positioning System Active Control Network. PositioNZ allows you to download GPS 30 second RINEX files from the active control stations, which you can use with remote GPS station data to determine precise positions in terms of New Zealand Geodetic Datum 2000.

The network comprises around 38 stations in New Zealand, the Chatham Islands and Antarctica.

Recent new sites

This year, LINZ has commissioned two new PositioNZ stations. The first was located south of Warkworth where the Auckland University of Technology has recently built a new VLBI radio telescope. The second is two kilometres from Whakatane, and fills a gap in the network in the eastern Bay of Plenty.

Economic analysis

LINZ recently commissioned an analysis of the economic benefits of upgrading the PositioNZ network to enable the provision of real-time services. This report found that the national economic benefits from upgrading the PositioNZ network are considerable. It also recommended that this data is made available to all parties free of charge. We are hoping to have this service available to the public by the end of the year. This data can be used by third party providers to generate network-based RTK corrections, possibly by adding data from their own stations.

Read the full report, prepared by McKenzie Podmore Ltd, on Economic Issues Regarding LINZ Conversion of its Precision Reference Network to Real Time Status (PDF 97KB).

1" streams

As a result of this economic analysis, LINZ has begun upgrading the communications technologies used to transfer data from the PositioNZ sites. This will enable the data to be transferred reliably and in a more timely manner. LINZ is hoping to begin making this real-time GPS data freely available via the internet by the end of the year from several sites. Users should then be able to obtain single-base RTK correction streams from these sites over the internet using a cellular connection and an RTK capable GNSS receiver. The only cost to the user would be from mobile data charges related to their cellular service.

GNSS capability

LINZ is looking to upgrade the receivers at its PositioNZ stations to GNSS capability over the next few years. We will be undertaking an evaluation of GNSS receivers within the next 12 months. Following this, sites throughout the country will be upgraded with priority given to those stations closest to populated areas.

PositioNZ-PP

LINZ is in the final stages of developing a GPS post processing service called PositioNZ-PP. This service will use the GPS station data from PositioNZ to compute precise coordinate solutions for the supplied user GPS Receiver Independent Exchange Format (RINEX) data. RINEX is an open plain text data interchange format for raw satellite observation data. The aim is to provide a simple but powerful service that makes the geodetic infrastructure ‘invisible’ to the user. The user does not need to observe multiple stations in the field to obtain a precise position because the PositioNZ reference stations are used. The service will also produce NZGD2000 coordinates for the user stations without having to connect into the geodetic network.

The service once launched will be able to simultaneously process multiple RINEX files. A minimum of one hour of GPS (GLONASS, Global Navigation Satellite System, is not processed) dual-frequency L1/L2 data will be required. GLONASS is a satellite navigation system similar to the GPS system developed by the former Soviet Union and is now Russian government operated. The web application will require the user to log in to the LINZ website, upload the RINEX data, and then enter the site's antenna information. The user will then submit the job and service will process the job, emailing the results back once completed. The results report will include site coordinates in NZGD2000 and NZTM, as well as quality information and processing options used. The user will also have access to a SINEX (Solution Independent Exchange Format) file for inclusion into other processing and adjustment packages. Users will also have the ability to log back into the website to retrieve processing reports from past jobs.

The backend engine room for the service will use Bernese, which is a high precision scientific GNSS data processing software package. Once launched, the service will only compute solutions in "Static Mode" at an observation interval of 30 seconds. This means large observation data spans are required. Best results are typically obtained with six hours of data. LINZ, however, will be looking to implement "Rapid Static" processing after the service goes live.

A significant feature for the PositioNZ-PP will be the ability for users to determine NZGD2000 coordinates without having to connect into the geodetic network. All GPS processing will be done in terms of ITRF (International Terrestrial Reference Frame) at the epoch of the supplied user data, then using the LINZ deformation model and a transformation from ITRF to NZGD2000, an epoch 2000.0 coordinate will be produced. Further details on this extract transform method can be found in section 5 of a GNS consultancy report (PDF 1.5MB).

PositioNZ-PP is part of a collaborative project between Geosciences Australia and LINZ, which looks to improve the usability, functionality and latency of the existing AUSPOS service (Australian Positioning Service).

Media enquiries: Brad Young, Land Information New Zealand, phone +64 4 460 0147, email media@linz.govt.nz